In general, a liquid crystal display device displays images including letters, still images, moving images and so on. To display those images, the liquid crystal display device precisely controls a minute area of a liquid crystal. The light transmissivity of the liquid crystal varies in accordance with the strength of an electric field applied thereto.
The liquid crystal display device generally includes a transparent pixel electrode, a transparent common electrode, and a liquid crystal formed between the two electrodes. The pixel electrode formed on a transparent substrate is divided to have a matrix shape and to form minute regions on the transparent substrate. An electric power is applied to the pixel electrode. The common electrode is formed on the whole surface of another transparent substrate.
The liquid crystal display device can display images by precisely controlling the strength of the electric power applied to the pixel electrode while an electric power is applied to the common electrode as a reference electric power. In this case, the strength of the electric power applied to the pixel electrode is controlled by a thin film transistor manufactured by a semiconductor technology.
The thin film transistor includes a gate electrode, a channel layer formed over the gate electrode and insulated from the gate electrode, a source electrode, and a drain electrode. The source and the drain electrodes are formed to not be electrically short with the channel layer.
The pixel electrode is electrically connected to the drain electrode of the thin film transistor. Also, the electric power is applied to the source electrode of the thin film transistor so as to be applied to the pixel electrode, and an electric power for turning on the thin film transistor is applied to the gate electrode of the thin film transistor so that the electric power is applied from the source electrode to the drain electrode on a pertinent time.
The resolution of the liquid crystal display device is determined by the integration degree of the pixel electrodes. For example, when the liquid crystal display device displays full color images with a resolution of 800×600 in a unit effective display region, the number of the pixel electrodes should be 800×600×3, and the number of the thin film transistors should match with that of the pixel electrodes.
FIG. 1 is a schematic plane view explaining the conventional method for driving a liquid crystal display device.
Referring to FIG. 1, thin film transistors 30 are arranged on a substrate 40 in a matrix shape, and gate electrodes, which is arranged along each row of the matrix, of all the thin film transistors 30 are connected to a gate line 10. Also, source electrodes, which are arranged along each column of the matrix, of all the transistors 30 are connected to a data line 20.
To apply predetermined electric power to each pixel electrode, electric power is applied to a first, second, third, . . . , and last data line. While the electric power is applied to each data line 20, a first gate line 10 is selected, and then a threshold voltage (Vth) is applied to the selected first gate line 10. Hence, all the thin film transistors 30 connected to the first gate line 10 are turned on. According to the turn-on of the thin film transistor 30, the electric power applied to the source electrode is applied to the pixel electrode via a drain electrode.
Thus, an electric field is formed between the pixel electrode and a common electrode. In this case, a liquid crystal is arranged by the electric field, and then a light can pass through the liquid crystal after a predetermined time. The amount of the light passing the liquid crystal varies in accordance with the arrangement of the liquid crystal. Then, the light passed the liquid crystal progresses to a color pixel. Such process is sequentially performed in the first, second, third, . . . and last gate line during one frame. A user can recognize a still image or the moving image because the frame is very rapidly executed for one second.
However, the liquid crystal display device having those construction and operation mechanism may not accurately display the moving image. The liquid crystal display device can display the moving image when a response speed and an operation speed of the liquid crystal are equal to or faster than the number of the frames of the moving image.
When the liquid crystal has a slow response speed and a lower operation speed, the liquid crystal display device cannot display the moving image. In particular, the image spread phenomenon and the image distortion phenomenon may occur because the liquid crystal is not sufficiently arranged when the response speed and the operation speed of the liquid crystal are low.
Recently, the response speed and the operation speed of the liquid crystal have been improved so that the liquid crystal display device can display the moving image.
However, there are limits to enhance the response speed and the operation speed of the liquid crystal, so a frame frequency should be at least doubly increased than that of the present liquid crystal display device in order to display more precise moving image. For example, the frequency demanded for displaying the precise moving image should be about 120 Hz when the present frame frequency is approximately 60 Hz.
However, if the frame frequency increases, a point of time when the driving signal is applied to the gate electrode and another point of time of the data driving signal is applied to the source electrode should be changed, and also other driving signal such as a timing driving signal should be varied. As a result, the constructions of the hardware of the liquid crystal display device should be altered.
Particularly, when the frame frequency is high, the above-mentioned problem cannot be solved basically since the period demanded for processing one frame is exceedingly reduced and the response speed of the liquid crystal should be high. In addition, the liquid crystal display device may not accurately display the moving image according as the liquid crystal display device has a high resolution.
In the meantime, according to another method for displaying the moving image through the liquid crystal display device, the screen of the liquid crystal display is maintained black for a predetermined time, which is similar to a driving method of a cathode ray tube (CRT) type display device.
FIG. 2 is a graph showing a period during which a light is supplied in one frame when the conventional liquid crystal display device operates.
Referring to FIG. 2, for example, when the liquid crystal display panel requires a totally approximately 16.7 msec in order to display all images during one frame, all thin film transistors should be turned on within approximately 8 msec to arrange the liquid crystal before the light is supplied to the liquid crystal, and then the light is supplied to the liquid crystal only during the residuary period of approximately 8.7 msec.
In the above-described method, however, the period for processing one frame includes the period for turning on all thin film transistors and the period for supplying the light to the liquid crystal. This method has a disadvantage that the brightness is greatly reduced to deteriorate the display quality of the image according as the screen of the liquid crystal display device becomes large, or according as the number of the thin film transistor increases.